The goal of the proposed studies is to determine the genetic origins of potentially nephritogenic IgG autoantibodies in SLE. It has previously been demonstrated that the IgG that form immune deposits in renal lesions in lupus are enriched for autoreactivity and polyreactivity. This suggest that these pathogenic Ig may share common variable (V) region sequences. To define the genetic origins of these V regions, we will evaluate antigen binding and V gene usage of a large panel of hybridomas and M Ab derived from the in vivo activated splenic B cells of lupus- prone MRL-lpr/lpr mice of different ages. Reactivity of individual M Ab to selected antigens will be determined by ELISA, and VH gene usage will be detected by hybridization of radiolabelled V gene family probes to whole cell RNA. This will allow us to characterize the life history of autoantibodies in lupus, to detect changes associated with the development of disease, and identify Ig that share properties with nephritogenic Ig. From among these latter Ig, we can identify Ig injected with the Ig of interest. We will subsequently determine the nucleotide sequences of V regions of these Ig using Sanger dideoxy sequencing of cloned cDNA. From the results it should be possible to answer several questions regarding the gene origins of autoantibodies in SLE: 1) Do IG that share properties with nephritogenic Ig, or that autoantibodies encoded by germline V genes, or do they arise by somatic mutation? 3) Do certain V genes preferentially encode autoantibodies, and the Ig that are potentially nephritogenic?